(a) Field of the Invention
The present invention relates to the method of manufacturing bobbins applied to sewing machines.
(b) Description of Prior Art
In prior methods of manufacturing bobbins for sewing machines, there have heretofore been two generally categorized methods, such as method of cutting the whole bobbin body and method of welding flanges to bobbin shaft. In said cut work method, as shown in Japanese Patent Publication NO.48-9610, bobbins are machined out from metallic pole. And in said welding work method, flanges formed by press working etc. are welded or caulked to bobbin shaft which is machined out in advance.
And the method of utilizing laser beam machines for machining a large number of workpieces is disclosed, as shown in U.S. Pat. No. 4,760,237, which comprises stationary guide means, a first table movably mounted on the stationary guide means for moving between two positions, a movable guide means liftably disposed, and a second table movably mounted on the movable guide means for movement between the two positions. However, nothing is disclosed therein about the solution to the problem inherent to welding bobbin material. Steel bobbin in general needs to be plated on the surface because of its poor corrosion resistance. On the contrary, aluminum bobbin, for example, is comparatively light and surpasses steel bobbin in corrosion resistance. There have heretofore been, however, such problems that the method of cutting alminum bobbin requires many processes therein, in addition to such exteremely low yield that the weight of finished product is only about one tenth of that of original material. On the other hand, the above-mentioned methods of welding work have had their own problems. That is, bobbins have low intensity if manufactured by means of the caulk method and even have holes or deformations in the welded portion if manufactured by means of the electric welding, which is mainly caused by comparatively low melting point of aluminum and has prevented the electric welding method from being embodied.
One solution for overcoming these problems, for example, is to utilize laser beam as welding means. Nevertheless, conventional laser beam machines have not been applied to welding alminum material, as already shown in U.S. Pat. No. 4,760,237, which discloses nothing about the method of welding alminum material by means of laser beam.